Long ago, dinosaurs ruled the Earth. Then, suddenly, they died out. For thousands of years, no one knew these giant creatures had ever existed. Then people began finding fossils--bones and teeth and footprints that had turned to stone. Today, teams of experts work together to dig dinosaur fossils out of the ground, bone by fragile bone. Then they put the skeletons together again inside museums, to look just like the dinosaurs of millions of years ago.